Origin

An Old English word from an ancient root shared by Latin dens, the source of dental (late 16th century), dentist (mid 18th century), trident (late 16th century) ‘three teeth’, and indent. To fight tooth and nail was in the 16th century to fight with tooth and nail. Although in a real fight this would mean ‘by biting and scratching’, the phrase is almost always used of non-physical struggles. To set someone's teeth on edge is to cause them intense irritation. The expression comes from the Bible, and expresses the unpleasant sensation felt when you have bitten into something that is bitter or sour: ‘Every man that hath eaten the sour grape, his teeth shall be set on edge’ (Jeremiah). See also hen